The term “flexible cable,” as used herein, means any flexible, elongated, energy or fluid-conducting device, such as a cable composed of one or more electrical wires or optical fibers, a fluid-conducting hose for conducting compressed air or a hydraulic fluid used as a medium for transmission of motive power, a flexible conduit used to convey a gas, a liquid, or another fluid material for use in a machine or industrial process, a flexible actuator such as a Bowden wire, or a flexible rotating shaft with or without a non-rotating sheath. Such flexible cables are used, for example, to connect relatively moving parts of a machine such as a machine tool, an industrial robot, or a conveyor or other material-handling or material-carrying machine, such as a hoist or other machine used in a civil engineering application.
When a flexible cable is connected to a moving part, torsion, flexion, and tensile forces applied to the cable as a result of movement of the moving part can result in damage to, or distortion of, the cable. Cable guides have been used to avoid damage and distortion of the cables.
As shown in FIG. 10, a typical cable guide 100 is composed of a number of links, each comprising a pair of side plates 102 disposed on both sides of a cable C, and connecting rods or plates 101 connecting the side plates. The connecting plates 101 form bridges connecting the side plates of the cable guide both above and below the cable, and, together with the side plates 102, form an elongated channel through which the cable C extends. The side plates 102 on each side of the guide are hinged to one another so that the guide can bend at least in a single plane. Usually, the flexion of the guide is limited to a specific minimum radius of curvature in order to avoid kinking of the cable C.
Typically, the cable guide has a fixed end 105 and a moving end 106. Where a cable guide of sufficient length is folded on itself by a bend 120 as shown in FIG. 5, it is possible for two portions of the guide to come into face-to-face contact with each other. Friction between the contacting parts of the guide can obstruct smooth reciprocating motion. Moreover, frictional contact over time can cause wear and eventual breakage of the cable guide. Breakage can also result from interference between projecting portions of the two facing parts of the guide.
To avoid the problems resulting from frictional contact between facing parts of a folded cable guide, a skate can be interposed between the facing parts. As illustrated in FIG. 7, a skate 300 is sandwiched between two facing parts of the cable guide, preventing direct contact between the facing parts. A typical conventional skate is depicted and described in United States Patent Application Publication 2005/0155337, dated Jul. 21, 2005.
Alternatively, a plurality of supporting rolls can be provided on upper and lower parts of a frame disposed between facing portions of a folded cable guide, as shown in Japanese Patent Publication No. Sho. 57-16273. In this case, the rollers on the upper and lower parts of the frame are disposed at equal intervals, and each roller on the upper part of the frame has a corresponding roller directly below it on the lower part of the frame.
The skate 300 of FIG. 7 includes pairs of rollers disposed between upper and lower parts of the cable guide. As shown in FIG. 8, the skate includes a pair of side frames 33 in which the rollers are rotatable, and a base 340, which maintains a predetermined widthwise distance between the side frames 330.
A skate 300 of the kind illustrated in FIG. 7 can be used with a long cable guide 100, where the opposed parts of the cable guide face each other over a long distance, even as much as several tens of meters. Since the cable guide 100 comprises interconnected, molded, links, accumulation of slight differences between the pitches of the right and left portions of the links can lead to lateral flexion in the guide 100, as illustrated in FIG. 9. Excessive lateral flexion of the guide from the ideal position, represented by the two parallel broken lines, can cause the guide 100 to come off from the skate 300.
When the cable C accommodated within the cable guide 100 is out of balance in the widthwise direction, the cable guide can snake. Furthermore, with a long skate, it is difficult to establish parallelism between a guide rail on which the fixed end 105 of the cable guide 100 is mounted, and a movable machine, or portion of a machine, attached to the movable end 106 of the guide. Thus, the guide 100 can move in a slanted relationship to the rollers 320, generating a force that acts laterally on the rollers 320. As a result, slip is generated between the rollers 320 and the cable guide 100. The slip prevents the skate 300 from moving smoothly, and generates a longitudinal shift of the skate relative to the cable guide. When the longitudinal shifts of the skate accumulate due to repeated reciprocation of the movable part of the guide, the guide can eventually collide with the skate. In the worst case, the skate 300, or the cable guide 100, can become deformed or damaged.
The rollers 320 of the skate 300 are sandwiched between upper and lower parts of a cable guide or between independent upper and lower cable guides. When the skate is to be removed from maintenance, it is typically taken out in the direction indicated by the arrow F in the enlarged part of FIG. 7. A large amount of sliding resistance is generated at contact points X and Y, between the rollers 320 and the upper and lower parts of the guide. Therefore, a large force is needed to draw the skate 300 out from between the upper and lower parts of the guide. The large drawing force required for removal of the skate can be reduced by lifting the upper part of the guide so that the skate can roll easily on the lower part of the guide. However, because of the difficulty encountered in lifting the upper part of a guide, raising the upper part of the guide does not make it significantly easier to remove the skate for maintenance.
In the skate described in Japanese Patent Publication No. Sho. 57-16273, where independent rollers are provided on upper and lower parts of a skate frame, removal of the skate from between opposed parts of a cable guide is easier than in the case of the skate of U.S. Patent Application Publication 2005/0155337. However, the skate described in the Japanese patent publication requires a large vertical space between the opposed parts of the cable guide.
An object of this invention is to provide a compact skate for a cable guide, which increases the useful life and endurance of the cable guide, and which can be removed readily and easily for maintenance.